THE ROLE OF SMECTITE IN THE CLOGGING MECH ANISM OF MICROCRACKS - EXAMPLE OF WATER HAWAIITE INTERACTION/

Percolation tests of heated aqueous fluids (90 and 150 degrees C, Q = 0.1 mL.mn(-1), confining pressure P-c =1 MPa), in an open system, thro ugh fractured hawaiite have shown the primordial role of smectitic cla y minerals in the behaviour of the microcracks. The decrease of the pe rmeability (1.3 - 1.5.10(-15) to 1-3.10(-16)m(2)) are provoked by CU t he decompression and hydration of the smectitic matrix of the the meso stasis (10 % of the rock) and (2) by the precipitation of iron oxides inside these newly porous smectitic matrices which build local and dis semimated bridges of smectite + Fe oxides between the two wall-rocks. (C) Academie des sciences/Elsevier, Paris.